Blue Streak Cleaner Wrasse
The blue streak cleaner wrasse (Labroides dimidiatusis) is a small, beautiful marine fish from the family Labridae. It reaches a maximum adult size of only about 4 inches (10 cm). Because it is the most commonly encountered cleaner wrasse species, it is commonly referred to simply as "cleaner wrasse."
It name is derived from it coloration as well as its behavior. The cleaner wrasse is the smaller fish in the photo above. It is hovering over a golden damselfish that it is about to clean. As the name "cleaner wrasse" suggests, this fish provides a cleaning service for other reef fish. Specifically, the cleaner wrasse cleans the parasites off of other marine fish. In fact, this is how the blue streak cleaner wrasse and other species of cleaner wrasses sustain themselves in their natural habitat.
Unfortunately, cleaner wrasses usually don't survive long in captivity. The blue streak cleaner wrasse is more hardy than many of the other cleaner wrasse species, but still doesn't do well in captivity.
This is because there usually isn't enough fish with parasites on them in the home aquarium to sustain the cleaner wrasse. They will sometimes accept substitute foods, but not always. Substitute foods for them are live black worms, frozen fish food for marine fish, mysis and brine shrimp, and chopped seafood. Despite feeding cleaner wrasses these substitute foods, they often don't survive long and die of starvation or malnutrition shortly after being brought into captivity.
Because they tend to do so poorly in captivity it is recommended not to keep this and other species of cleaner wrasses in your aquarium.
If you are interested in a cleaner fish, there are other fish and invertebrates that perform a "cleaning service" that fare much better in captivity than cleaner wrasses, such as the cleaner gobies and cleaner shrimps.
Despite the cleaner wrasses poor survival rate in captivity, you'll often find them for sale. Because they are so difficult to properly feed I would suggest NOT purchasing these fish and removing from their natural environment where they are happy and healthy. I've seen at least one online retailer that has these fish for sale that won't even guarantee their live arrival.